The progressive improvement of electronic systems, such as microcontroller and microprocessor based applications for the control of motors, as well as the availability of improved portable power sources, has made the development of more efficient electric motor drives a compelling challenge. Electronically controlled pulsed energization of windings of motors offers the prospect of more flexible management of motor characteristics. By control of pulse width, duty cycle, and switched application of a power source to appropriate stator windings, functional versatility that is virtually indistinguishable from alternating current synchronous motor operation can be achieved. The use of permanent magnets in conjunction with such windings is advantageous in limiting current consumption.
The above-identified copending related U.S. patent application of Maslov et al., Ser. No. 09/826,423, identifies and addresses the need for an improved motor amenable to simplified manufacture and capable of efficient and flexible operating characteristics. It is highly desirable to attain smooth operation over a wide speed range, while maintaining a high torque output capability at minimum power consumption. The copending related U.S. applications incorporate electromagnet poles as isolated magnetically permeable structures configured in an annular ring, relatively thin in the radial direction, to provide advantageous effects. With this arrangement, flux can be concentrated, with virtually no loss or deleterious transformer interference effects in the electromagnet cores, as compared with prior art embodiments. While improvements in torque characteristics and efficiency are attainable with the structure of the identified copending application, further improvements remain desirable.
The Maslov et al. applications recognize that isolation of the electromagnet groups permits individual concentration of flux in the magnetic cores of the groups, with low flux loss and no deleterious transformer interference effects with other electromagnet members. Operational advantages can be gained by configuring a single pole pair as an isolated electromagnet group. Magnetic path isolation of the individual pole pair from other pole groups eliminates a flux transformer effect on an adjacent group when the energization of the pole pair windings is switched.
Copending related U.S. patent application of Maslov et al., Ser. No. 09/966,101 describes benefits to be gained from utilization of three dimensional aspects of motor structure. Advantages are recognized from the use of materials such as a soft magnetically permeable medium that is amenable to formation of a variety of particular shapes. For example, core material may be manufactured from soft magnet grades of Fe, SiFe, SiFeCo, SiFeP powder material, each of which has a unique power loss, permeability and saturation level. Core geometries and core dimensions of stator elements, with relevant tolerances, can be formed without the need to form laminations and thus optimize the magnetic potential gradient developed between coupled poles of rotor permanent magnets and stator electromagnets. A structural configuration is disclosed wherein axially aligned stator poles and axially aligned rotor magnets provide highly concentrated flux distribution. Such configuration provides a greater number of poles with the same individual active air gap surface areas and/or greater total active air gap surface area than conventional motors having the same air gap diameter.
In summary, concentration of flux, maximization of flux, minimization of flux loss and transformer interference effects, are all contributing factors in the attainment of efficient motor operation with high torque capability. Motor structural configurations in which multiple poles are in axial alignment to provide efficient operation at high torque output have been described in the above-identified copending applications. Such arrangements, due to the relatively great volume occupied by the large number of stator core elements and rotor poles, are advantageous for use in environments in which space and weight considerations are not at a premium. There is a continuing need for motor structural configurations that provide these improved attributes as well as economy of size and geometry.
The above-identified copending Maslov et al. application, addresses these needs by development of motor structural configurations to increase the surface areas of opposing stator poles and rotor poles across a plurality of air gaps. The relatively larger surfaces in which flux can be concentrated promote high torque capacity. These concepts are further structurally developed in the present invention.